WordPress at a glance
function is not described

wp_send_new_user_notifications() WP 4.4.0

Initiates email notifications related to the creation of new users.

Notifications are sent both to the site admin and to the newly created user.

No Hooks.

Return

Null. Nothing.

Usage

wp_send_new_user_notifications( $user_id, $notify );
$user_id(int) (required)
ID of the newly created user.
$notify(string)
Type of notification that should happen. Accepts 'admin' or an empty string (admin only), 'user', or 'both' (admin and user).
Default: 'both'

Changelog

Since 4.4.0 Introduced.
Since 4.6.0 Converted the $notify parameter to accept 'user' for sending notifications only to the user created.

Code of wp_send_new_user_notifications() WP 5.5.1

<?php
function wp_send_new_user_notifications( $user_id, $notify = 'both' ) {
	wp_new_user_notification( $user_id, null, $notify );
}